The field of the disclosure is related to systems and methods for controlling small particles. More particularly, the disclosure relates to systems and methods for trapping particles using projected light.
In the field of quantum computation, the performance of quantum bits (“qubits”) has advanced rapidly in recent years, with various multi-qubit implementations aiming toward scalable architectures. In contrast to classical computational methods that rely on binary data stored in the form of definite on/off states, or bits, methods in quantum computation take advantage of the quantum mechanical nature of quantum systems, where each qubit can be in a superposition of multiple states. For example, in some applications, qubits can be composed of individual atoms whose quantum states can be controlled and accessed using optical confinement techniques. By manipulating a collection of many qubits, multiple calculations can be performed effectively at the same time, providing enormous computational speed-up capabilities, and impacting areas associated with complex computational problems, such as cryptography, search, simulations, and so on.
Specifically, optical sources can be used to provide periodic or aperiodic potentials, or optical lattices, where particles, such as individual atoms or molecules, can become trapped via the Stark effect. The resulting arrangements of particles, can resemble artificial crystals that are free from defects. Advantageously, these can be utilized to investigate fundamental principles governing interactions and material properties, including quantum phase transitions and quantum spin dynamics, as well as provide promising systems for storing and processing quantum information. Particularly, such systems facilitate the ability to localize and act on an ensemble of identical particles, which can be described by a well-understood quantum structure.
In many applications, neutral atoms have been implemented as promising candidates for quantum information processing due to their well-defined quantum structure and charge neutrality. Particularly, charge neutrality isolates the atoms from charge-related perturbations, and leads to reduced decoherence. In addition, neutral atoms arranged in an optical lattice are unique for quantum information applications, as they afford single particle control, and can be scaled to large qubit systems.
Atomic trapping using optical sources is achieved due to the coherent interactions of applied electromagnetic (“EM”) fields and induced oscillating electric dipole moments. Specifically, internal atomic energy shifts occur due to source EM fields, resulting in effective potentials from which confinement forces arise. Generally, optical source wavelengths are shifted, or detuned, with respect to atomic resonances, wherein induced atomic dipole moments within the atom are in-phase for “red” detuning and 180° out-of-phase for “blue” detuning of trapping light field and atomic resonance frequency. Particularly, when a light source frequency is below an atomic transition frequency, or red detuned, respective atoms are attracted to the intensity maxima of the light field created with a strength dependent upon the detuning magnitude, whereas they are repelled from it in the case of blue detuning. Additionally, the potential depth, or strength of attraction, can be modified by controlling the intensity, or power, generated by the optical sources.
Commonly, optical lattices potentials are formed by interference patterns of light fields generated using multiple optical sources. Such patterns, consisting of dark and bright regions in space, are projected onto small particles in order to achieve spatial confinement, where generally, the particles are pre-cooled to temperatures in the microKelvin range. For example, a one-dimensional (“1D”) optical lattice can be created by superposing two counter-propagating laser beams such that an optical standing wave is created. Additionally, higher dimensional optical lattices, such as two-(“2D”) and three-dimensional (“3D”) structures, necessitate additional optical sources. For example, as shown in FIG. 1, a simple-cubic lattice structure can be produced by overlapping three orthogonal standing waves formed using 3 pairs of counter-propagating optical sources, while for a 2D optical lattice, the atoms are confined to an array of tightly confining 1D potential tubes using 2 paired sources. In some cases, to generate more complex lattice configurations, the geometry of trapping potentials can be modified by interfering laser beams under different angles.
However, positions of atoms in an optical lattice generated by interference of counter-propagating beams, or beams co-propagating at a small angles, are directly sensitive to optical path-length drifts, causing differential phase shifts between beams. Although such shifts can be, in principle, compensated by using active stabilization techniques, this has, at best, been attempted using single-atom implementations. As such, extending such active stabilization to multi-atom systems adds substantial system complexity.
Given the above, there is a need for systems and methods directed to small particle confinement using optical trapping lattices that are scalable to a large number of sites, minimize crosstalk from neighboring planes of trapped particles, and are stable against position drifts due to optical phase fluctuations.